BACKGROUND: Venom allergen-like proteins (VALs) are abundant in the excretory-secretory products (ESPs) of numerous parasitic helminths and have been extensively studied for over 30 years because of their potential to interact with host systems. Despite substantial research, however, the precise functions of these proteins remain largely unresolved. Schistosomes, parasites of the circulatory system, are no exception, with 29 SmVAL genes identified in the genome of Schistosoma mansoni to date. The eggs of these parasites, as primary pathogenic agents, interact directly with host tissues and release excretory-secretory products that aid their egress from the host. Although SmVALs have been detected in the egg secretome in the past, direct evidence of their secretion and functional interaction with host molecules has never been demonstrated. These findings fuel the ongoing debate as to whether egg-expressed SmVALs interact with the mammalian host or are rather miracidial proteins synthesized within the egg during larval development. RESULTS: Based on complete revision of the SmVAL family and an associated robust transcriptomic meta-analysis of gene expression across the life cycle, we show that many of SmVAL genes, including 6 newly identified genes, are expressed in the infective larvae-producing stages (eggs and sporocysts). Following localization of two "egg-specific" SmVAL9 and SmVAL29 did not prove active secretion of these molecules into surrounding tissues but were aligned with miracidial structures interfacing with the molluscan host, specifically the larval surface and penetration glands. Finally, we show the complete lack of interactions between candidate SmVAL proteins and an array of 755 human cell receptors via a state-of-the-art SAVEXIS screen. CONCLUSIONS: Overall, we conclude that these "egg" SmVALs are not involved in direct host‒parasite interactions in the mammalian host and are rather proteins employed during intermediate host invasion. Our study revisits and updates the SmVAL gene family, highlighting the limitations of in silico protein function predictions while emphasizing the need for up-to-date datasets and tools together with experimental validation in host-parasite interactions. By uncovering the diversity, expression patterns, and interaction dynamics of SmVALs, we open new avenues for understanding host manipulation and reevaluating orthologous proteins in other helminths.

• Keywords
• CAP, Egg, Miracidium, SAVEXIS, SCP, Schistosomiasis, Transcriptome, Venom allergen-like,
• MeSH
• Allergens * genetics   metabolism   MeSH
• Host-Parasite Interactions * genetics   MeSH
• Humans MeSH
• Ovum * metabolism   MeSH
• Helminth Proteins * genetics   metabolism   MeSH
• Schistosoma mansoni * genetics   metabolism   MeSH
• Gene Expression Profiling MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Allergens * MeSH
• Helminth Proteins * MeSH

Schistosomula (the post-infective stages) of the neurotropic schistosome Trichobilharzia regenti possess multiple isoforms of cathepsin B1 peptidase (TrCB1.1-TrCB1.6) with involvement in nutrient digestion. The comparison of substrate preferences of TrCB1.1 and TrCB1.4 showed that TrCB1.4 had a very narrow substrate specificity and after processing it was less effective toward protein substrates when compared to TrCB1.1. Self-processing of both isoforms could be facilitated by sulfated polysaccharides due to a specific binding motif in the pro-sequence. Trans-activation by heterologous enzymes was also successfully employed. Expression profiling revealed a high level of transcription of genes encoding the enzymatically inactive paralogs TrCB1.5 and TrCB1.6. The transcription level of TrCB1.6 was comparable with that of TrCB1.1 and TrCB1.2, the most abundant active isoforms. Recombinant TrCB1.6wt, a wild type paralog with a Cys29-to-Gly substitution in the active site that renders the enzyme inactive, was processed by the active TrCB1 forms and by an asparaginyl endopeptidase. Although TrCB1.6wt lacked hydrolytic activity, endopeptidase, but not dipeptidase, activity could be restored by mutating Gly29 to Cys29. The lack of exopeptidase activity may be due to other mutations, such as His110-to-Asn in the occluding loop and Asp224-to-Gly in the main body of the mature TrCB1.6, which do not occur in the active isoforms TrCB1.1 and TrCB1.4 with exopeptidase activity. The catalytically active enzymes and the inactive TrCB1.6 paralog formed complexes with chicken cystatin, thus supporting experimentally the hypothesis that inactive paralogs could potentially regulate the activity of the active forms or protect them from being inhibited by host inhibitors. The effect on cell viability and nitric oxide production by selected immune cells observed for TrCB1.1 was not confirmed for TrCB1.6. We show here that the active isoforms of TrCB1 have different affinities for peptide substrates thereby facilitating diversity in protein-derived nutrition for the parasite. The inactive paralogs are unexpectedly highly expressed and one of them retains the ability to bind cystatins, likely due to specific mutations in the occluding loop and the enzyme body. This suggests a role in sequestration of inhibitors and protection of active cysteine peptidases.

• Keywords
• cathepsin B, cystatin, helminth, occluding loop, peptidase, processing, schistosome, substrate specificity,
• MeSH
• Astrocytes metabolism   MeSH
• Cystatins metabolism   MeSH
• Hydrolysis MeSH
• Isoenzymes metabolism   MeSH
• Cathepsin B chemistry   genetics   metabolism   MeSH
• Macrophages metabolism   MeSH
• Mice MeSH
• Nitric Oxide metabolism   MeSH
• Enzyme Precursors metabolism   MeSH
• Proteolysis MeSH
• RAW 264.7 Cells MeSH
• Recombinant Proteins metabolism   MeSH
• Schistosomatidae enzymology   pathogenicity   MeSH
• Amino Acid Substitution MeSH
• Substrate Specificity MeSH
• Protein Binding MeSH
• Cell Survival MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• cystatin, egg-white MeSH Browser
• Cystatins MeSH
• Isoenzymes MeSH
• Cathepsin B MeSH
• Nitric Oxide MeSH
• Enzyme Precursors MeSH
• Recombinant Proteins MeSH

BACKGROUND: Helminth neuroinfections represent a serious health problem, but host immune mechanisms in the nervous tissue often remain undiscovered. This study aims at in vitro characterization of the response of murine astrocytes and microglia exposed to Trichobilharzia regenti which is a neuropathogenic schistosome migrating through the central nervous system of vertebrate hosts. Trichobilharzia regenti infects birds and mammals in which it may cause severe neuromotor impairment. This study was focused on astrocytes and microglia as these are immunocompetent cells of the nervous tissue and their activation was recently observed in T. regenti-infected mice. RESULTS: Primary astrocytes and microglia were exposed to several stimulants of T. regenti origin. Living schistosomulum-like stages caused increased secretion of IL-6 in astrocyte cultures, but no changes in nitric oxide (NO) production were noticed. Nevertheless, elevated parasite mortality was observed in these cultures. Soluble fraction of the homogenate from schistosomulum-like stages stimulated NO production by both astrocytes and microglia, and IL-6 and TNF-α secretion in astrocyte cultures. Similarly, recombinant cathepsins B1.1 and B2 triggered IL-6 and TNF-α release in astrocyte and microglia cultures, and NO production in astrocyte cultures. Stimulants had no effect on production of anti-inflammatory cytokines IL-10 or TGF-β1. CONCLUSIONS: Both astrocytes and microglia are capable of production of NO and proinflammatory cytokines IL-6 and TNF-α following in vitro exposure to various stimulants of T. regenti origin. Astrocytes might be involved in triggering the tissue inflammation in the early phase of T. regenti infection and are proposed to participate in destruction of migrating schistosomula. However, NO is not the major factor responsible for parasite damage. Both astrocytes and microglia can be responsible for the nervous tissue pathology and maintaining the ongoing inflammation since they are a source of NO and proinflammatory cytokines which are released after exposure to parasite antigens.

• Keywords
• Anti-inflammatory cytokines, Astrocytes, Avian schistosome, Cathepsin B, Microglia, Neuroinfection, Nitric oxide, Proinflammatory cytokines, Trichobilharzia regenti,
• MeSH
• Astrocytes immunology   parasitology   MeSH
• Interleukin-6 metabolism   MeSH
• Cells, Cultured MeSH
• Mice MeSH
• Neuroglia immunology   parasitology   MeSH
• Nitric Oxide metabolism   MeSH
• Schistosomatidae immunology   MeSH
• Tumor Necrosis Factor-alpha metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• interleukin-6, mouse MeSH Browser
• Interleukin-6 MeSH
• Nitric Oxide MeSH
• Tumor Necrosis Factor-alpha MeSH

To date, most molecular investigations of schistosomatids have focused principally on blood flukes (schistosomes) of humans. Despite the clinical importance of cercarial dermatitis in humans caused by Trichobilharzia regenti and the serious neuropathologic disease that this parasite causes in its permissive avian hosts and accidental mammalian hosts, almost nothing is known about the molecular aspects of how this fluke invades its hosts, migrates in host tissues and how it interacts with its hosts' immune system. Here, we explored selected aspects using a transcriptomic-bioinformatic approach. To do this, we sequenced, assembled and annotated the transcriptome representing two consecutive life stages (cercariae and schistosomula) of T. regenti involved in the first phases of infection of the avian host. We identified key biological and metabolic pathways specific to each of these two developmental stages and also undertook comparative analyses using data available for taxonomically related blood flukes of the genus Schistosoma. Detailed comparative analyses revealed the unique involvement of carbohydrate metabolism, translation and amino acid metabolism, and calcium in T. regenti cercariae during their invasion and in growth and development, as well as the roles of cell adhesion molecules, microaerobic metabolism (citrate cycle and oxidative phosphorylation), peptidases (cathepsins) and other histolytic and lysozomal proteins in schistosomula during their particular migration in neural tissues of the avian host. In conclusion, the present transcriptomic exploration provides new and significant insights into the molecular biology of T. regenti, which should underpin future genomic and proteomic investigations of T. regenti and, importantly, provides a useful starting point for a range of comparative studies of schistosomatids and other trematodes.

• MeSH
• Adaptation, Biological * MeSH
• Host-Pathogen Interactions * MeSH
• Ducks parasitology   MeSH
• Metabolic Networks and Pathways genetics   MeSH
• Molecular Sequence Data MeSH
• Schistosomatidae genetics   growth & development   MeSH
• Sequence Analysis, DNA MeSH
• Life Cycle Stages MeSH
• Gene Expression Profiling * MeSH
• Computational Biology * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Cercarial dermatitis (swimmer's itch) is a condition caused by infective larvae (cercariae) of a species-rich group of mammalian and avian schistosomes. Over the last decade, it has been reported in areas that previously had few or no cases of dermatitis and is thus considered an emerging disease. It is obvious that avian schistosomes are responsible for the majority of reported dermatitis outbreaks around the world, and thus they are the primary focus of this review. Although they infect humans, they do not mature and usually die in the skin. Experimental infections of avian schistosomes in mice show that in previously exposed hosts, there is a strong skin immune reaction that kills the schistosome. However, penetration of larvae into naive mice can result in temporary migration from the skin. This is of particular interest because the worms are able to migrate to different organs, for example, the lungs in the case of visceral schistosomes and the central nervous system in the case of nasal schistosomes. The risk of such migration and accompanying disorders needs to be clarified for humans and animals of interest (e.g., dogs). Herein we compiled the most comprehensive review of the diversity, immunology, and epidemiology of avian schistosomes causing cercarial dermatitis.

• MeSH
• Biodiversity MeSH
• Disease Outbreaks MeSH
• Host Specificity MeSH
• Humans MeSH
• Bird Diseases parasitology   transmission   MeSH
• Skin Diseases, Parasitic epidemiology   immunology   parasitology   prevention & control   MeSH
• Birds MeSH
• Schistosomiasis epidemiology   immunology   parasitology   prevention & control   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Cercarial dermatitis (swimmer's itch) is a common non-communicable water-borne disease. It is caused by penetration of the skin by larvae (cercariae) of schistosomatid flukes and develops as a maculopapular skin eruption after repeated contacts with the parasites. The number of outbreaks of the disease is increasing, and cercarial dermatitis can therefore be considered as an emerging problem. Swimmer's itch is mostly associated with larvae of the bird schistosomes of Trichobilharzia spp. Recent results have shown that mammalian infections (including man) manifest themselves as an allergic reaction which is able to trap and eliminate parasites in the skin. Studies on mammals experimentally infected by bird schistosome cercariae revealed, however, that during primary infection, parasites are able to escape from the skin to the lungs or central nervous system. This review covers basic information on detection of the infectious agents in the field and the clinical course of the disease, including other pathologies which may develop after infection by cercariae, and diagnosis of the disease.

• MeSH
• Central Nervous System microbiology   MeSH
• Cercaria immunology   MeSH
• Dermatitis diagnosis   immunology   parasitology   MeSH
• Skin microbiology   pathology   MeSH
• Humans MeSH
• Disease Models, Animal MeSH
• Swimming MeSH
• Lung microbiology   MeSH
• Schistosoma MeSH
• Schistosomiasis complications   diagnosis   immunology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH